Power management is used in many devices and systems to improve power efficiency, helping to reduce power consumption and/or heat dissipation. For battery-powered mobile devices and systems, power management can help extend operation.
Some platform-level power management has been based on some heuristics collected on the platform and some guidance given by an operating system. Processor utilization can be used as a rough estimate of platform activity. When there is heavy input/output (I/O) activity and light processor utilization, however, the platform will be put into lower power states, impacting I/O performance. Indeed, as a platform goes into deeper power states, its response latency to break events like direct memory access (DMA) accesses and interrupts increases. Although many I/O devices are designed to tolerate some fixed minimum response latency from the platform, this can effectively limit the depth of power states which the platform may enter. The platform would compromise functionality and/or performance if the platform entered a deeper power state that increased its response latency beyond the fixed minimum an I/O device could tolerate.
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